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https://issues.apache.org/jira/browse/LUCENE-8982?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17223986#comment-17223986
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Zach Chen commented on LUCENE-8982:
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Thanks Michael! I've opened an initial PR with the proposed changes, but also
have a few follow-up questions:
# Are new unit tests (other than benchmarking tests) needed, given these
changes may not have direct side-effects to assert on?
# Shall I go ahead and remove code that may no longer be used after these
changes, such as the related method in `NativePosixUtil.cpp`?
The PR also needs to include some more updates to comment to reflect the new
way of doing direct IO. I can work on that once the changes are very much
ready.
> Make NativeUnixDirectory pure java now that direct IO is possible
> -----------------------------------------------------------------
>
> Key: LUCENE-8982
> URL: https://issues.apache.org/jira/browse/LUCENE-8982
> Project: Lucene - Core
> Issue Type: Improvement
> Components: modules/misc
> Reporter: Michael McCandless
> Priority: Major
>
> {{NativeUnixDirectory}} is a {{Directory}} implementation that uses direct IO
> to write newly merged segments. Direct IO bypasses the kernel's buffer cache
> and write cache, making merge writes "invisible" to the kernel, though the
> reads for merging the N segments are still going through the kernel.
> But today, {{NativeUnixDirectory}} uses a small JNI wrapper to access the
> {{O_DIRECT}} flag to {{open}} ... since JDK9 we can now pass that flag in
> pure java code, so we should now fix {{NativeUnixDirectory}} to not use JNI
> anymore.
> We should also run some more realistic benchmarks seeing if this option
> really helps nodes that are doing concurrent indexing (merging) and searching.
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